Important properties of such mortars are good processability of the fresh mortar together with, in the cured mortar compositions, high flexibility and impact resistance, good adhesion to various mineral substrates such as concrete, renders, underlayments, screeds but also tiles and various organic substrates such as insulation materials, in particular to polystyrene boards.
To set an optimal property profile, the formulations on which the adhesive mortars are based are therefore modified with thermoplastic polymers based on ethylenically unsaturated monomers. Dry mortars containing mineral binders are frequently modified with water-redispersible polymer powders based on the abovementioned thermoplastic polymers. This polymer modification gives mortar compositions which meet the above requirements.
In US 2007/0256600 A1, phosphate monoesters, diesters and triesters are used as adhesion promoter for this purpose. However, the high price of these additives and the poor workability of the resulting mortars is a disadvantage.
Improving the adhesion to polystyrene substrates by addition of aromatic polyethers is known from EP 0698586 A1. A disadvantage here is that ecological concerns about the use of such compounds have arisen and the poor workability of the resulting mortars.
It was therefore an object of the invention to improve the adhesion of mortars comprising water-redispersible polymer powders to inorganic and organic substrates, particularly to expanded polystyrene and to mineral wool, and to overcome the abovementioned disadvantages.
Polypropylene oxide (polypropylene glycol) is known as shrinkage-reducing additive from EP 0573036 B1. DE-A 1935507 mentions polypropylene glycol as antifoam for mortar compositions or concrete compositions. In WO 01/04212 A1, a combination of phenol-formaldehyde condensate and polyoxyalkylene compounds is used for improving the redispersibility of water-redispersible polymer powders.
U.S. Pat. No. 4,654,085 discloses an additive combination of cellulose ether, starch ether and polyacrylamide for the improvement of sag resistance in cementitious compositions. EP 1840098 A2 discloses the use of methyl starch ethers for the improvement of the adhesion of mineral binder compositions.